The present invention relates to a refrigeration unit, for example for use in a refrigerator or freezer for storing food, or for other cooling applications and chambers for cooling items. In this specification, the term refrigeration unit is used to describe the components that achieve cooling, and the term refrigerator covers the cabinet or compartment that is cooled or frozen by the cooling of the refrigeration unit.
Most commercial refrigeration systems make use of the vapour compression refrigeration cycle for cooling. This relies on the compression-condensation-expansion-evaporation cycle of refrigerant fluid. Essentially, a refrigerant fluid is expanded, for example by passing this through a throttle, thereby reducing the pressure and consequently the boiling point of the refrigerant fluid. In this state, the refrigerant fluid is able easily to evaporate and thereby absorb heat energy. In particular, heat energy can be absorbed from the refrigerator. The resulting superheated, vaporised refrigerant is then compressed in a compressor. This compression increases the pressure of the refrigerant fluid, thereby increasing its boiling point. The resulting high-pressure vapour is then condensed, causing the refrigerant fluid to give up the heat energy absorbed during the evaporation. This heat energy is emitted to the atmosphere. The refrigerant fluid, having given up all of the absorbed heat energy, is then again expanded by the throttle, reducing the pressure and therefore enabling the refrigerant to absorb further heat energy as it is evaporated as the cycle is repeated.
To make use of this cycle, a conventional refrigeration unit comprises an evaporator over which the air within the refrigerator cabinet is blown and through which expanded, low pressure, refrigerant fluid is passed. The refrigerant absorbs heat energy from the air, and therefore reduces the temperature within the cabinet. The refrigerant is then conveyed from the evaporator to a compressor where the fluid is compressed, and the resulting high-pressure vapour is condensed within the condenser, causing the absorbed energy to be dissipated from the refrigerant fluid to the atmosphere.
In many commercial refrigeration systems, the refrigeration cabinet is formed with an opening in the top through which the air is cycled and cooled. It has been known since the early 1980""s to locate the components of the refrigeration unit in a plug-in box that is mounted as a single component on top of the cabinet to allow communication with the interior of the cabinet for cooling the air in the cabinet. This has the advantage that, in the event of failure of the refrigeration unit, it is possible merely to replace the entire plug-in refrigeration unit as a single component.
There are a number of problems with the use of such unitary, plug-box type refrigeration units. Firstly, such boxes are difficult and time consuming to construct. As the air from within the refrigeration cabinet passes through the plug-in box to allow cooling of the air, it is important that the box gives good thermal insulation to prevent heat from the atmosphere warming the air within the chamber. Therefore, it is usual to form the box in a similar way to the rest of the refrigerator cabinet, namely to form an outer metallic shell, an inner metallic shell spaced from the outer shell, and to fill the void between the inner and outer shells with an insulating foam material. This assembly requires the separate formation of the inner and outer shells, and the installation of spacers to ensure the required spacing between the shells. The opening between the inner and outer shells must then be sealed, for example using tape, to ensure that the void is properly filled with foam to the required density for the insulation properties required. There is a special need for good seals due to the high pressure required to inject the insulating foam to the required density. Furthermore, the high pressure used means that both the inner and outer skins must be supported during foam filling. Once the shell has been filled with the insulating foam, other components, such as baffles, must be installed individually within the box for directing airflow through the unit and past the evaporator. Components must also be added to support the parts of the refrigeration system, such as the evaporator, fans and tubes. Holes must be formed through the shell to receive the tubing for the refrigerant and power lines for the electrical components. These components cannot be installed prior to foam filling due to the need to support the inside shell during high-pressure foam filling. Accordingly, there are a large number of individual components that must be installed separately, resulting in a lot of time spent in assembling the unit. This results in a significant cost.
A second problem is that the each of the components used in the refrigeration unit itself, such as the condenser, fan, evaporator, must be individually installed in the unit, and attached to the shell by bolts or the like. Each of these components must individually be sealed to prevent any leakage of refrigerant or of the air being cooled. Again, this is time consuming and results in high manufacturing costs.
A third problem is that the design of the inside of the unit is limited due to the use of sheet metal to form the unit, and due to the need to mount components of the refrigeration unit within the box. In particular, this limits greatly the control of airflow through the unit, preventing optimisation of this. Also, it is difficult to ensure airtight seals, and so there is a risk of leakage from the desired flow path.
A fourth problem with existing designs is apparent when the units require repair. Whilst the use of a plug box allows the unit as a whole to be removed easily for replacement, in many cases it is preferred to merely repair or replace individual failed components, or to gain access to remove debris. As the boxes are formed with an open bottom, through which air flows from and to the refrigeration cabinet via the open top of the cabinet, but with solid sides, back, front and top, the only way to service the unit is through the bottom opening. When the unit is installed, this means that the only access to the inside of the unit, without removing this from the cabinet, is from the inside of the refrigerator cabinet. This means that it is necessary to empty the refrigerator cabinet to allow access to the inside of the unit. This may be inconvenient, for example in a busy kitchen where there may be nowhere else to store the contents of a refrigerator that is being repaired. Even where it is possible to empty the refrigerator, it is difficult to work inside the unit due to the limited access.
According to a first aspect of the present invention, a box for a refrigeration unit comprises a moulded, hollow walled, plastics shell, the walls of which are filled with an insulating material.
According to a second aspect of the present invention, a refrigeration unit comprises a first heat exchanger for absorbing thermal energy in fluid communication with a second heat exchanger for dissipating the absorbed thermal energy, and a means for blowing fluid to be cooled into or over the first heat exchanger such that a refrigerant passing through the first heat exchanger absorbs thermal energy from the fluid, in which the first heat exchanger is located within a box according to the first aspect of the present invention, the box further including a first opening through which the fluid to be cooled can enter the box to the heat exchanger, and a second opening through which the cooled fluid can exit the box.
An advantage of the use of a moulded plastics box is that the box may be formed automatically as a single component. This greatly reduces the amount of time required to build the box, and therefore greatly reduces the cost of manufacture of the box. A further advantage of moulding the box as a single unit is that there is no need to seal joints between components forming the box as is required with boxes formed of sheet material to ensure that the shell can be filled without leaking of the insulation material. This has the advantage of reducing the manufacturing time, both as it avoids the need to manually seal the joints and as there is no need to spend time cleaning the excess foam that leaks from the box, and reduces material costs as there is reduced wastage of insulation material.
Preferably the shell is formed by a rotational moulding technique. In such a moulding technique, a mould is formed having surfaces corresponding to the desired surfaces of the shell, and this is filled with granulated plastics material from which the shell is to be formed. The mould is then heated, causing the plastics material in contact with, or close to, the surface of the mould to melt. During this period, the mould is rotated slowly about three axes. This ensures that the molten plastics material evenly coats the surface of the mould. The mould is then cooled and the plastics shell removed. Using rotation-moulding techniques allows the shell to be accurately formed with the required wall thickness. This is especially advantageous for the later fixing of components to the shell.
The box is preferably formed with an upper opening, closeable with a separate lid. This is of considerable benefit as it allows access to the inside of the box for repair or replacement of the components of the refrigeration unit from above a refrigerator cabinet on which the unit is installed. The advantages of this are firstly that there is no need to empty the contents of the refrigeration cabinet before access to the inside of the refrigeration unit can be achieved, and secondly as access from above the unit is much less awkward than through the open bottom of the unit as is required by the prior art. Where the plug box is made from sheet metal shells filled with foam, it is difficult to form the box with a separate lid, and in particular to form the box with a separate lid that maintains the desired thermal properties of the unit. In particular, it would be difficult to form an opening in the shell box into which a lid can be fitted, and difficult to form a suitable lid with the required insulation which can be reliably fitted into the opening. It is for this reason that the prior art plug boxes have been formed with a solid top, and a bottom opening that is not sealed, through which both the air from the cabinet passes and through which access to the inside of the unit can be made. Where the box is formed with a separate lid, the lid is preferably also formed as a hollow plastics shell, preferably by rotation moulding, filled with insulation to give the required thermal properties.
An advantage of forming the box with a separate lid is that the components of the refrigeration unit may more easily be placed in position. This is of particular advantage for the pipes interconnecting the components inside the box with those outside. By providing recesses for the pipes in the top of the wall of the box that are covered by the lid, the pipes, even when connected to further components, may merely be lowered into place. This compares to the conventional arrangement where pipes would need to be fed carefully through small holes in the shell wall, making fitting of pipes and components a very difficult and time-consuming operation.
The box preferably includes an exposed portion or platform for those parts of the refrigeration unit which require exposure to the atmosphere, in particular the second heat exchanger. The second heat exchanger is required to dissipate heat from the refrigerant fluid. It is therefore important that these components of the second heat exchanger are separated from the first heat exchanger that extracts heat from the fluid into the refrigerant. The components of the refrigeration unit mounted outside the shell are preferably mounted on a substrate, and the substrate is mounted to the exposed portion or platform of the box.
Advantageously, the first heat exchanger includes an evaporator through which the refrigerant passes, the refrigerant absorbing thermal energy as this is evaporated. An expander may be provided upstream of the evaporator to decrease the pressure, and therefore the boiling point, of the refrigerant.
The second heat exchanger preferably comprises a condenser to condense the refrigerant and thereby dissipate heat. A compressor may be provided upstream of the condenser to increase the pressure and boiling point of the refrigerant.
The plug box is advantageously formed with air guides that are arranged to direct fluid, usually air, from the refrigeration cabinet over the first heat exchanger provided within the plug box and back into the refrigeration cabinet. The air guides preferably include a funnel to direct the air from a large area towards a fan or other means for passing the fluid to the first heat exchanger. The use of a moulded plastics box has a considerable advantage over sheet metal boxes in this regard in that they permit much greater freedom of design for the air guides that is not possible with sheet metal boxes. Further, as the box is moulded as a single unit from plastics material, this ensures that there is no leakage of air as may be the case for a sheet metal box, and therefore all air drawn from the refrigeration chamber passes over the heat exchanger before being returned to the cabinet.
To minimise the energy required to circulate the air, the heat exchanger advantageously has a large surface area, thereby minimising the pressure difference across the heat exchanger.
Depending upon the application, additional evaporators may be provided in the refrigeration unit, and/or additional compressors and/or condensers provided.
According to a third aspect of the present invention, a refrigerator comprises a cabinet to be cooled, the cabinet having an upper opening, and a refrigeration unit according to the second aspect of the present invention mounted above the upper opening, such that, in use, air from within the cabinet is passed into the refrigeration unit where the air is cooled, and from which the cooled air is returned to the cabinet.